Working out the number of minutes between two dates

[TheBalance]

Using MySql 3 (deliberately using an old version) how can I work out the difference between a date in a database field (stored as a unix time) and now. I'm actually using PostNuke and want to identify how long open items have been in my phpbb forum.

I've tried various forms and the last effort was :
select to_days(now())-to_days(from_unixtime(p.post_time)) from nuke_phpbb_posts p

but that gives my a lowest number of 176 (I know people have been using it today).

any pointers much appreciated.

Thanks